Field of the Invention
An embodiment of the present invention relates to a particle beam treatment apparatus that irradiates an affected area of a patient with a charged particle beam to treat the affected area.
Description of the Related Art
A particle beam treatment technique of setting an irradiation target center (isocenter) to an affected area (such as a cancer-affected area) of a patient and irradiating the affected area with an ion beam of protons, carbon ions, or the like has been widely known.
For example, a particle beam treatment apparatus used for this treatment includes an ion beam generation apparatus, a beam transport system, and an irradiation apparatus installed in a rotating gantry.
An ion beam accelerated by the ion beam generation apparatus reaches the irradiation apparatus through the beam transport system, and an affected area of a patient is irradiated with the ion beam from the irradiation apparatus. On this occasion, the irradiation apparatus rotates around the patient along with a rotation of the rotating gantry, whereby the irradiation apparatus can irradiate the affected area with the ion beam on the basis of an irradiation angle determined by a treatment plan. In order to reduce damage to normal tissue around the affected area by the ion beam, it is necessary to precisely irradiate the affected area with the ion beam. For this purpose, it is important to perform precise positioning of a particle beam irradiation unit and precise positioning of the affected area of the patient with respect to the particle beam irradiation unit.
In general, a gantry body portion to which the irradiation apparatus is provided has a structure with rigidity that is sufficient to suppress a displacement of a magnet mounting portion and precisely irradiate the affected area with the ion beam. Such a conventional technique is disclosed in, for example, Japanese Patent Laid-Open No. 2014-113419.
In the rotating gantry of the above-mentioned conventional technique, if the rigidity of the gantry body portion is not sufficient, the displacement of the magnet mounting portion and three-dimensional whirling accuracy (irradiation target center accuracy) of a position of irradiation from the irradiation apparatus to the irradiation target center may have variations of about a few millimeters along with a rotation of the rotating gantry. As a result, there arises a problem that an enormous amount of time is required for positioning of the patient at the time of treatment irradiation, depending on the irradiation angle.
If a thickness of the gantry body portion is increased or a reinforcement member is added in order to enhance the rigidity of the body portion, increase in weight and manufacturing cost occurs. In addition, such increase in weight leads to increase in moment of inertia, so that braking time in emergency situations may become longer.